As a resin pipe joint of this kind, a tube joint disclosed in Patent Literature 1 is known. Namely, the tube joint is structured in the following manner. A synthetic resin-made tube (1) is forcedly pressed onto a fitting cylinder (5) of a joint body (4), or, as shown in FIG. 2 of Patent Literature 1, a tube end portion (2) is previously flared and then fitted to the fitting cylinder (5). Then, a union nut (6) which is previously fitted to the tube is screwed with the joint body, and forcedly moved in the axial direction of the joint body (4) by performing a fastening operation, whereby a flaring base portion (2a) of the tube (1) is strongly pressed in the axial direction by an edge portion (6a) to seal between the tube (1) and the fitting cylinder (5).
As a structure similar to the above-described one, also a resin pipe joint disclosed in FIGS. 8 and 9 of Patent Literature 2 is known. As disclosed in FIG. 5 of Patent Literature 2 and Patent Literature 3, also a resin pipe joint having a structure in which an end of a tube that is flared and externally fitted to an inner ring is internally fitted to a fitting cylinder of a joint body, and a portion of the tube that is flared to the inner ring is pressed by fastening a union nut to attain a sealing function is known. Both the joints have the structure where a tube end is flared and a sealing function is attained by fastening a union nut. In the former structure in which the tip end of the tube is externally fitted to the fitting cylinder to fix the nut, there is an advantage that a pipe joint can be economically configured by two components or the joint body and the union nut. In the latter structure using the inner ring, there are advantages that leakage can be surely avoided and a stable performance is obtained, and that the reliability is high.
In actual work on a resin pipe joint having such various excellent advantages, there is an item which is always requested to be improved, i.e., that the timing when the fastening of the union nut is ended cannot be clearly known. In a resin-made joint, originally, the fastening torque in an operation of turning a union nut is gradually increased because of the characteristics of the material, and therefore a sense of fastening up which is caused by a sudden increase of the fastening torque is poor unlike the case where a metal material is used, so that the end of fastening is hardly sensuously known. In the case of insufficient fastening, leakage may occur, and, in the case of excessive fastening, the joint may be broken. Such disadvantages are easily caused because the joint is made of a resin. Therefore, fastening of the union nut must be correctly ended.
In the case where a pipe joint is exposedly disposed in a state where the worker can see the whole joint, for example, the position of the screw advancement due to fastening of a union nut can be checked, so that it is relatively easy to know that the fastening end state is attained, or that such a state is approximately attained. In a place where a pipe joint is disposed, such as a narrow gap between other apparatuses, or a hidden place under the roof, a situation where it is impossible or difficult to see the joint often occurs, and the work of fastening the union nut is often performed in a blind manner. Even when the joint cannot be seen, therefore, it is required that the end or near end of the work of fastening the union nut is informed to the worker by any means.
Therefore, Patent Literature 3 discloses a technique in which, at just before the end of fastening of a union nut (2), a projection piece (15) that is projected in the axial direction from a joint body (1) in a cantilevered state, and a projection (23) that is raisedly formed in an end portion of the union nut (2) in the axial direction approach and interfere with each other in the circumferential direction to butt against each other, and the worker can known the end or near end of the fastening, based on a flapping sound which is generated by the projection piece (15) at this time. Namely, sound generating means for informing the fastening end state to the worker by a sound is disclosed.